1. Field of the Invention
The invention relates to a system for air supply, and more particularly, to a system for supplying air to pressurized aircraft cabins.
2. Description of Relevant Art
Modern aviation with fast, high-flying aircraft requires pressurized cabins. On long range flights, the flying altitude is approximately 30,000 feet, which corresponds to approximately 10,000 meters. Since the outside pressure at 10,000 meters is only approximately 265 mb compared to 1,016 mb at sea level, the respective oxygen partial pressure is only 77 mb, assuming no change in air composition from sea level to altitude. Humans cannot survive in such thin air. Thus, aircraft are equipped with pressurized cabins. The current international convention is to have all aircraft cabin pressures at 737 mb. This corresponds to an altitude of approximately 8,500 feet or approximately 2,600 meters. The resulting high pressure differential between inside the cabin and outside the cabin at altitude poses a major task and problem for the construction of an aircraft pressure hull. The skin Is under considerable stress, and the fuselage is expanded. For economic reasons (improved fuel economy), higher cruising altitudes of approximately 40,000 feet are desirable. A trade-off arises between the increased fuel economy and the added weight to provide the required extra mechanical stability. An alternative approach consists of reducing the cabin pressure to, for example, 540 mb. This corresponds to an altitude of 16,400 feet, or approximately 5,000 meters. At this absolute air pressure, the respective oxygen partial pressure is only 113 mb, compared to 213 mb at a sea level ground pressure of 1,016 mb. Such low oxygen pressure would eventually cause most passengers to faint. To prevent passengers from experiencing oxygen deficiencies under conditions of sudden pressure loss, each aircraft is equipped with individual oxygen masks that drop from the overhead luggage compartment for fast and convenient application to the passengers' faces.